How is synchrony identified in the visual analysis of neonatal electroencephalogram (EEG)?

Answer

Synchrony: Synchronous activity is defined as simultaneous EEG activity in homologous regions of each hemisphere. Synchrony is assessed during TA and NREM sleep. In well-established TA in healthy FT infants, the bursting activities between hemispheres occur almost simultaneously. In younger infants (32-38 weeks' postconceptional age), these bursts occur with less synchrony. In even younger PT infants (27-28 weeks' postconceptional age), the bursts of TD are synchronous between hemispheres.

Artifacts and a low-voltage record. A full-term infant aged 4 days with anoxia at birth and seizures. No spontaneous respirations occur. The record is low voltage with no activity of cerebral origin greater than 2 mV. All other activity can be accounted for by physiologic or nonphysiologic artifacts. ECG artifacts are diffuse. Pulse artifact is time locked to the ECG. An IV artifact occurs in multiple electrodes every 1.75 seconds and is most prominent in the right electrooculogram (REOG). The RESP channel demonstrates mechanical ventilation artifact.

Twitching artifact. A full-term, 3-day-old infant with anoxic encephalopathy and episodes of generalized twitching that last 1-2 seconds at a time. Muscle artifacts are seen in multiple electrodes and are particularly prominent in the EMG channel. After the twitch, the background attenuates and appears to be a state change rather than an electrographic seizure correlate.

Quiet sleep and tracé alternant (TA). An infant of 39 weeks' postconceptional age with hydrocephalus and possible seizures. During quiet sleep, respirations are regular, EMG activity is low-voltage tonic with no phasic activity, and no spontaneous eye movements occur. TA is seen with medium- to high-voltage mixed frequencies alternating with periods of relative voltage attenuation.

Active sleep. An otherwise healthy infant of 41 weeks' postconceptional age with episodes of arm and leg extension without EEG correlates. This segment of normal, active sleep shows irregular respirations; frequent eye movements on EOG; and a mixed pattern of delta, theta, and alpha frequency activity.

Tracé discontinu (TD). An infant of 24 weeks' gestational age at age 4 weeks with an intraventricular hemorrhage and left shoulder twitching. Periods of alternating high-voltage mixed frequencies and periods of voltage suppression are normal findings before 28-30 weeks' postconceptional age.

Burst suppression. An infant of 42 weeks' postconceptional age with asphyxia. An alternating pattern of high-voltage mixed frequency activity and voltage attenuation in a term infant indicates severe diffuse cerebral dysfunction. Compare this to tracé discontinue (TD), in which similar activity may be considered normal prior to 30 weeks' gestational age.

Voltage attenuation, focal. An infant of 40 weeks' postconceptional age with a left middle cerebral artery infarction and intermittent posturing and hyperextension of the neck. Background activity demonstrates attenuation of delta and fast activity on the left indicative of a structural lesion on the left.

Positive temporal sharps. An infant of 41 weeks' postconceptional age with a fever (temperature, 102°F) and 3 episodes of right arm and leg jerking with eye deviation that last 5-10 seconds each. Left positive temporal sharps are seen in the 4th and 5th seconds at T3 and independently at T4 during the 8th second.

Excessive sharp transients. An infant of 36 weeks' postconceptional age with hypoxic ischemic encephalopathy and seizures on days 2 and 3 of life. Sharp transients are seen in the 1st and 3rd seconds at T4.

Alternating seizure 1. An infant of 32 weeks' gestational age at 40 weeks' conception with serratia meningoencephalitis. Surgery for drainage and dural repair was performed. This seizure begins at 00:36:12 in the right posterior quadrant with sharply contoured rhythmic delta at 1.5-2 Hz. Note the compressed nature of the time base, with each gradation representing 1 second. By 00:36:50, the spread to the left posterior quadrant is evident. The seizure continues in the next figure.

Alternating seizure 2. In the first 10 seconds of the page, the electrographic seizure pattern in the right posterior quadrant attenuates, leaving behind the ongoing left posterior quadrant discharge. By 00:37:32, spread to T3 is evident. Seizures in neonates often alternate or "ping pong" from one side to the other.

Electrographic seizure, surface positive. An infant of 40 weeks' postconceptional age with partial seizures and hypocalcemia. An asymptomatic surface-positive electrographic seizure occurs at C4 with rhythmic spikes at 4 Hz.

Electrographic seizure, focal 1. An infant of 40 weeks' postconceptional age with meningitis. This page contains 2 minutes of compressed EEG to demonstrate the entire extent of the seizure. At 00:37:32, repetitive T4 spikes begin, and, over the next 10 seconds, they become rhythmic spikes. This spreads centrally, and, by 00:39:05, the discharge begins to end with slow spike discharges at T4 and then completely attenuates.

Electrographic seizure focal 2. Expanded time base of seizure onset from the previous image. In the 2nd second, a clear rhythmic spike onset is seen in the right temporal region.

Pseudo theta. An infant of 35 weeks' gestational age at age 3 days. Patient is having alternating jerking movements of all 4 extremities. Focal monorhythmic theta at 7 Hz is seen in the right temporal and left central regions, independently.

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